Assessing exposure to cosmic radiation on board aircraft.

The assessment of exposure to cosmic radiation on board aircraft is one of the preoccupations of organizations responsible for radiation protection. The cosmic radiation particle flux increases with altitude and latitude and depends on the solar activity. The radiation exposure has been estimated on several airlines using transatlantic, Siberian and transequatorial routes on board subsonic and supersonic aircraft, to illustrate the effect of these parameters. Measurements have been obtained with a tissue equivalent proportional counter using the microdosimetric technique. Data have been collected at maximum solar activity in 1991-92 and at minimum in 1996-98. The lowest mean dose rate measured was 3 microSv/h during a Paris-Buenos Aires flight in 1991; the highest was 6.6 microSv/h during a Paris-Tokyo flight using a Siberian route and 9.7 microSv/h on Concorde in 1996-97. The mean quality factor is around 1.8. The corresponding annual effective dose, based on 700 hours of flight for subsonic aircraft and 300 hours for Concorde, can be estimated between 2 mSv for least-exposed routes and 5 mSv for more exposed routes.     

Performance and reliability of the NASA Biomass Production Chamber.

The Biomass Production Chamber (BPC) at the Kennedy Space Center is part of the Controlled Ecological Life Support System (CELSS) Breadboard Project. Plants are grown in a closed environment in an effort to quantify their contributions to the requirements for life support. Performance of this system is described. Also, in building this system, data from component and subsystem failures are being recorded. These data are used to identify problem areas in the design and implementation. The techniques used to measure the reliability will be useful in the design and construction of future CELSS. Possible methods for determining the reliability of a green plant, the primary component of a CELSS, are discussed.     

Oscillations of axial plant organs.

The tips of roots and shoots commonly show lateral movements as they grow forwards. These occur as both circumnutations (with long periods and large amplitudes) and micronutations (with short periods and small amplitudes). Their properties are reviewed, with emphasis on roots, and possible ways in which they could be regulated are discussed. The mechanisms could include long-range controls (for circumnutations) that depend on transmissible signals using steps common to gravitropism, and short-range controls (for micronutations) that operate within the elongation zone. The former are a property of the apex as a whole, while the latter may be confined to localized groups of cells. Simulation of nutations is presented with a view to isolating key physiological processes. However, this approach is limited by the current inadequate understanding of the growth mechanisms involved.     

A program to measure new energetic particle nuclear interaction cross sections.

The Transport Collaboration, consisting of researchers from institutions in France, Germany, Italy and the USA, has established a program to make new measurements of nuclear interaction cross sections for heavy projectiles (Z > or = 2) in targets of liquid H2, He and heavier materials. Such cross sections directly affect calculations of galactic and solar cosmic ray transport through matter and are needed for accurate radiation hazard assessment. To date, the collaboration has obtained data using the LBL Bevalac HISS facility with 20 projectiles from 4He to 58Ni in the energy range 393-910 MeV/nucleon. Preliminary results from the analysis of these data are presented here and compared to other measurements and to cross section prediction formulae.     

A baseband Doppler simulator for radar system development

Elementary electronics building blocks can be configured as a low-cost baseband Doppler simulator for developing the post-detector processing parts such as MTIs and MTDS of millimeter wave pulsed radars employing amplitude and phase channels. The challenge of narrow pulses in conjunction to low Doppler frequencies is handled here by CMOS switches and normal function generator ICs. Test noise is generated with an off-the-shelf radio RF/IF circuit. Wideband video amplifiers are not required. Typical performance figures include pulse widths from 50 ns, target ranges from 0 to ambiguity maximum, target velocities from 0.5 m/s to 500 m/s and PRFs up to 100 kflz. Virtual target RCS can be adjusted as needed in a straightforward way.     

A two-dimensional position-sensitive spectroscopic proportional counter for balloon-borne hard X-ray astronomy

A new design of position sensitive spectroscopic proportional counter is described, for use in a balloon borne hard x-ray telescope. Initial position and spectral resolution data from a one-dimensional laboratory prototype are reported. With this device, the final telescope will have an angular resolution of better than 10 minutes of arc.     

SDI

The President's Strategic Defense Initiative (SDI) began in 1983 following his historic March 23, 1983 speech. The SDI program has enjoyed substantial progress since this beginning. As the SDI begins its fourth year, the outlines of a basic system architecture, feasible for deployment in the 1990s, begins to emerge. In addition, SDI technical progress shows great promise not only for an initial strategic defense system, but also for maintaining defense effectiveness into the first decades of the next century against countermeasures designed specifically to defeat defenses.     

Advances in non-linear apodization

Selected new methods and applications of non-linear apodization for irregularly-shaped and parse coherent apertures and arrays are presented. The benefits include unproved impulse response performance, i.e., reduced peak sidelobes and integrated sidelobe power, along with improved mainlobe resolution, compared to classic windowing techniques. Nonlinear apodization (NLA) techniques can also serve as powerful engines for effective superresolution and bandwidth extrapolation of coherent data for filling sparse apertures. The sparse aperture filling property of superresolution algorithms for radar data forms the basis for a new concept which is introduced here: synthetic multiple aperture radar technology (SMART). Increased swath and/or reduced antenna size are some of the benefits postulated for SMART applied to synthetic aperture radar (SAR) systems. The benefits of these new methods and applications for nonlinear apodization are then demonstrated for two specific applications: 1) sidelobe control for Y-type synthetic aperture radiometers, such as the European Soil Moisture and Ocean Salinity (SMOS) system (Kerr et al.) and JPL's proposed GeoSTAR (Lambrigsten) concept; and, 2) filling of sparse synthetic aperture radar data by exploiting the bandwidth extrapolation properties of nonlinear apodization based superresolution techniques. The methods that have been developed and demonstrated herein have potential application to a wide range of passive and active microwave remote sensing and radar systems.     

Clover development during spaceflight: a model system.

The development of legume root nodules was studied as a model system for the examination of gravitational effects on plant root development. In order to examine whether rhizobial association with clover roots can be achieved in microgravity, experiments were performed aboard the KC-135 parabolic aircraft and aboard the sounding rocket mission Consort 3. Binding of rhizobia to roots and the initial stages of root nodule development successfully occurred in microgravity. Seedling germination experiments were performed in the sliding block device, the Materials Dispersion Apparatus, aboard STS-37. When significant hydration of the seeds was achieved, normal rates of germination and seedling development were observed.     

Space Station power requirements and issues

This paper provides an overview of the Space Station configuration and summarizes the requirements, architecture, and significant challenges associated with the electrical power system (EPS). The Space Station configuration was baselined during the systems design review (SDR) process in March, 1994. The current configuration includes the addition of Russia as an international partner, resulting in major changes to the assembly sequence, pressurized module complement, and overall power architecture. The Russian contributions to the power system architecture, as well as an-overview and development status of the US provided elements is presented. Finally, a planned flight demonstration of solar dynamic power system on the Mir as part of the first phase of US/Russian cooperation in human space flight is described